BlondieBC
Banned
Here's an interesting take on the consequences of Turtledove's TL-191. The writer suggests that economics would eventually demand that the UK flip-flop and seek an alliance with the US.
From here.
Another route to this dilemma is for the USA to make a lasting peace with the CSA and then annex Canada. Yes, the UK tended to flip allies fairly fast if needed, but I think the USA holds a grudge after it loses.